Abstract

Cerebral blood flow (CBF) during stepped hypercapnia was measured simultaneously
in the rat brain using near-infrared diffuse correlation spectroscopy (DCS) and
arterial spin labeling MRI (ASL). DCS and ASL CBF values agree very well, with
high correlation (R=0.86, p< 10-9), even when
physiological instability perturbed the vascular response. A partial volume
effect was evident in the smaller magnitude of the optical CBF response compared
to the MRI values (averaged over the cortical area), primarily due to the
inclusion of white matter in the optically sampled volume. The 8.2 and 11.7 mm
mid-separation channels of the multi-distance optical probe had the lowest
partial volume impact, reflecting ~75 % of the MR signal change. Using a
multiplicative correction factor, the ASL CBF could be predicted with no more
than 10% relative error, affording an opportunity for real-time relative
cerebral metabolism monitoring in conjunction with MR measurement of cerebral
blood volume using super paramagnetic contrast agents.

Figures (5)

Multi-modality probe design. a) Photograph of MRI head coil and
optical probe assembly on a rat, ready to be inserted into the
scanner bore; a separate ASL labeling coil is placed under the neck
area. b) Schematic of optical probe, with fibers connected to both
the FD-NIRS and the DCS system inserted at each location. Source
position is shown in red, while detector positions are in blue, with
source-detector separations of 5.3, 8.2, 11.7, and 15.5 mm,
respectively

Tables (3)

Table 1. Average relative CBF during stepped hypercapnia. Averages taken over the
second half of each hypercania period. Baseline value for MRI-ASL is
italicized to indicate lower confidence because of the lower SNR of the
corresponding raw data.

Metrics

Table 1.

Average relative CBF during stepped hypercapnia. Averages taken over the
second half of each hypercania period. Baseline value for MRI-ASL is
italicized to indicate lower confidence because of the lower SNR of the
corresponding raw data.

Table 3.

Error in predicting rCBF (normalized to CBF during the second half of the
2.5% CO2 period)

CO2
level

2.5%

5%

7.5%

Prediction

Rel. Err.

Prediction

Rel. Err.

Prediction

Rel. Err.

DCS Ch.2

100%

N/A

165%

9.93%

205%

-8.58%

DCS Ch.3

100%

N/A

165%

9.93%

206%

-7.98%

MRI-ASL

100%

N/A

150%

N/A

224%

N/A

Tables (3)

Table 1.

Average relative CBF during stepped hypercapnia. Averages taken over the
second half of each hypercania period. Baseline value for MRI-ASL is
italicized to indicate lower confidence because of the lower SNR of the
corresponding raw data.